The cloning of plant E2F, a retinoblastoma-binding protein, reveals uniqueand conserved features with animal G(1)/S regulators

Association of the retinoblastoma (Rb) protein with E2F transcription facto rs is central to cell cycle-specific gene expression and growth in animal c ells, Whether Rb-E2F complexes are also involved in plant cell growth and d ifferentiation is still unknown since E2F proteins have not yet been identi fied in plants, Here we report the isolation and characterisation of a whea t E2F (TmE2F) cDNA clone. Interestingly, the overall domain organisation of plant E2F is related to the human E2F-1/2/3 subset but its primary sequenc e is slightly more related to the E2F-4/5 subset, TmE2F-Rb binding depends on residues, located at the C-terminus, which are different from those of a nimal E2Fs, However, the acidic or hydrophobic nature of certain residues i s maintained, strongly suggesting that they may have a crucial role in E2F activities. Plant E2F is expressed in proliferating cultured cells and in d ifferentiated tissues and is up-regulated early in S phase, Our studies rei nforce the idea that G(1)/S regulators in plants are unrelated to those of yeast cells but similar to those of animal cells and provide new tools to a nalyse the links between cell cycle regulators, plant growth and developmen tal signals.